The mainstay of asthma treatment according to current NAEPP/NIH guidelines remains anti-inflammatory agents, of which corticosteroids are the most potent. However, long term administration of corticosteroids is associated with systemic side effects. Furthermore, some asthmatics are resistant to corticosteroids. Therefore, there is a need for new agents aimed at the inflammatory response in allergic airway disease.
The immune mechanism of asthma involves the polarized involvement of memory CD4+ T-helper cell with an imbalance of cells secreting type 2 (Th2) cytokines (interleukin (IL)-4, IL-5). The cytokine interferon-γ (INF-γ) is required for naive CD4+ lymphocyte differentiation to Th1 phenotype.
Airways inflammation in asthma is characterized by the presence of an increased number of eosinophils and activated CD4+ T cells. Asthma involves the polarized involvement of memory CD4+ T helper cells with an imbalance of cells secreting Th2-type cytokines over those secreting Th1-type cytokines. There is increased production of a number of cytokines including Type 2 cytokines IL-4 and IL-5, tumor necrosis factor (TNF-α), and granulocyte-macrophage colony-stimulating factor (GM-CSF) as well as tissue eosinophilia and increased IgE production. Most studies of cytokine profiles in airway inflammation come from the murine model of asthma. Animals are sensitized and challenged with antigen, usually ovalbumin and are found to have antigen specific IgE production, airway eosinophilia and airway hyperresponsiveness to aerosol antigen challenge. These changes are associated with increased Th2 cytokines and decreased INF-γ production (Brusselle et al., Am J Respir Cell Mol Biol, 1995 March; 12(3):254-259).
The Th2 cytokine IL-4 plays a prominent role in airway inflammation by promoting isotype switching of B cells to IgE synthesis and inducing naive T cell differentiation to Th2 lymphocytes. IL-4 knockout mice challenged with aerosolized antigen failed to produce specific IgE, airway hyperresponsiveness, airway eosinophilia, or Th2 cytokines in the airways (Brusselle et al., Am J Respir Cell Mol Biol, 1995 Mar; 12(3):254-259.) Wild-type mice treated with anti-IL-4 during the initial exposure to antigen but not during challenge inhibited IL-5 production and airways eosinophilia, whereas anti-IL-4 given during antigen challenge did not inhibit airways eosinophilia, indicating that IL-4 is essential for the induction of a local Th2 response (Coyle et al., Am J Respir Cell Mol Biol 1995 July; 13(1):54-59).
IL-10 is a cytokine produced by Th1 and Th2 lymphocytes, monocytes and macrophages, mast cells, keratinocytes, and eosinophils. IL-10 acts as an anti-inflammatory cytokine by downregulating the synthesis of proinflammatory cytokines by different cells, particularly monocytic cells. IL-10 downregulates the production of IL-5 by functionally inhibiting antigen presenting cells (APC) (Pretolani et al., Res Immunol 1997 January). A direct effect of IL-10 on eosinophil function has been demonstrated as well. Low concentrations of IL-10 were almost as active as corticosteroids in decreasing CD4 expression on eosinophils and accelerating cell death. GM-CSF is a cytokine directly involved in the homing and activation of eosinophils and neutrophils in inflamed tissues. Diminished levels of IL-10 production by PBMC and alveolar macrophages have been noted in asthmatic patients compared to normal controls (Borish, L et al., J Allergy Clin Immunol 1996 June; 97(6):1288-1296; Koning et al., Cytokine 1997 June; 9(6):427-436). In two models of allergic inflammation in mice, instillation of IL-10 protected sensitized mice from airway eosinophilia and neutrophilia possibly by inhibiting IL-5 and TNF-α (Zuany-Amorim et al., J Clin Invest 1996:2644-2651; Zuany-Amorim et al., J Immunol 1996 Jul. 1; 157(1):377-84).
Consistent with the Th2/Th1 dichotomy of cytokine production, murine models of asthma observe a cytokine profile of IL-4 and IL-5 predominance and low levels of the Th1 cytokines INF-γ and IL-12 (Ohkawara et al., Am J Respir Cell Mol Biol 1997 May; 16(5):510-20). Recent animal studies look at treatment with recombinant murine IL-12 in an attempt to reverse Th2 predominance. In vitro data indicate that the presence of IL-12 during the primary antigen stimulation of T-lymphocytes favors the development of Th1 cells (Kips et al., Am J Respir Crit Care Med 1996 February; 153(2):535-9). Kips confirmed this in vivo by administering IL-12 at the time of immunization and preventing production of specific IgE, airway eosinophilia, and airway hyperreactivity. Although, IL-12 administration during the aerosol challenge of already sensitized mice prevented airway eosinophilia and airway hyperresponsiveness, it did not decrease specific IgE production, suggesting that IL-12 stimulates the differentiation of naive Th cells into Th1 cells, and can suppress the development of Th2 cells. Inhibition of antigen induced airway eosinophilia by IL-12 is INF-γ dependent during the initial sensitization, but becomes INF-γ independent during the secondary challenge (Brusselle et al., Am J Respir Cell Mol Biol 1997 December; 17(6):767-71). In addition, mucosal gene transfer of IL-12 gene in the lung via vaccinia virus vector to sensitized mice prior to aeroallergen challenge has been demonstrated to lead to suppression of IL-4, IL-5, airway hyperresponsiveness, and airway eosinophilia in an INF-γ dependent manner (Hogan et al.,—Eur J Immunol 1998 February; 28(2):413-23).
Increasing INF-γ levels may drive the immune response to a Th1 phenotype and may be beneficial in asthma. Clinical correlation in humans has focused on cytokine levels in serum or stimulated PBMC. Most measurements of cytokines using stimulated PBMC have been performed in children. These studies have demonstrated an increased propensity towards IL-4 and IL-5 production and decreased production of INF-γ is asthmatic children. Furthermore, others have demonstrated an inverse association between atopy and/or asthma severity and release of INF-γ (Imada et al., (1995) Immunology 85(3): 373-80; Corrigan et al., (1990) Am Rev Respir Dis 141(4) Pt 1: 970-7; Leonard et al., (1997) Am J Respir Cell Mol Biol 17(3): 368-75; Kang et al., (1997) J Interferon Cytokine Res 17(8): 481-7). Cytokine levels in BAL fluid from asthmatic patients reveal low levels of INF-γ (Kang et al., (1997) J Interferon Cytokine Res 17(8): 481-7).
Clinical trials of rINF-γ in humans are few. As of 1999, INF-γ is indicated for the treatment of chronic granulomatous disease in which prolonged treatment (average duration 2.5 years) was associated with improvement in skin lesions, with minimal adverse events (fever, diarrhea, and flu-like illness) (N Engl J Med 324 (8):509-16; Bemiller et al. (1995) Blood Cells Mol Dis 21(3): 239-47; Weening et al., (1995) Eur J Pediatr 154(4): 295-8). Boguniewicz treated 5 patients with mild atopic asthma with escalating doses of aerosolized r INF-γ (maximum dose of 500 mcg, total study dose of 2400 mcg) delivered over 20 days (Boguniewicz et al., (1995) J Allergy Clin Immunol 95(1) Pt 1: 133-5). All patients tolerated the nebulized r INF-γ but there were no significant changes in the endpoints evaluated which included peak flow.
Nebulized r INF-γ was administered to 5 patients with persistent acid fast bacilli (AFB) smear and culture positive multiple-drug resistant tuberculosis (TB) (Condos et al., (1997) Lancet 349(9064): 1513-5). Patients received aerosol r INF-γ, 500 mcg, 3 times weekly for 4 weeks (total study dose 6000 mcg). Therapy was tolerated well with minimal side effects. At the end of the 4 weeks, 4 of the 5 patients were sputum AFB-smear negative and the time to positive culture increased indicating a reduced organism load after treatment. Interestingly, in these reported and in additional patients, PEFR performed 1 hour after treatment improved by 6% (n=10).
The idiopathic interstitial pneumonias have been grouped into seven categories based upon histology. They include usual interstitial pneumonia (UIP), non-specific interstitial pneumonia (NSIP), diffuse alveolar damage (DAD), organizing pneumonia (OP), desquamative interstitial pneumonia (DIP), respiratory bronchiolitis (RB), and lymphocytic interstitial pneumonia (LIP). See, e.g. Nicholson, Histopathology, 2002, 41, 381-391; White, J Pathol 2003, 201, 343-354.
The term “idiopathic pulmonary fibrosis” (IPF), synonymous with “cryptogenic fibrosing alveolitis” (CFA) is the clinical term for a major subgroup of the idiopathic interstitial pneumonias, and it describes a disease characterized by idiopathic progressive interstitial disease with a mean survival from the onset of dyspnea of 3 to 6 years. A diagnosis of idiopathic pulmonary fibrosis is made by identifying usual interstitial pneumonia (UIP) on lung biopsy. The histological pattern is characterized by heterogeneity that includes patchy chronic inflammation (alveolitis), progressive injury (small aggregates of proliferating myofibroblasts and fibroblasts, termed fibroblastic foci) and fibrosis (dense collagen and honeycomb change). (See, e.g. King et al., 2000, Am J of Resp. and Critical Care Med., 164, 1025-1032). Treatment of another subgroup of interstitial pneumonia is not predictive of successful therapy for idiopathic interstitial fibrosis.
Corticosteroids and cytotoxic agents have been a mainstay of therapy, with only 10-30% of patients showing an initial transient response, suggesting the need for long-term therapy (Mapel et al. (1996) Chest 110:1058-1067; Raghu et al. (1991) Am. Rev. Respir. Dis. 144:291-296). Due to the poor prognosis of patients with idiopathic pulmonary fibrosis, new therapeutic approaches are needed.
Interferons are a family of naturally-occurring proteins that are produced by cells of the immune system. Three classes of interferons have been identified, alpha, beta and gamma. Each class has different effects though their activities overlap. Together, the interferons direct the immune system's attack on viruses, bacteria, tumors and other foreign substances that may invade the body. Once interferons have detected and attacked a foreign substance, they alter it by slowing, blocking, or changing its growth or function.
Interferon-γ is a pleiotropic cytokine that has specific immune-modulating effects, e.g. activation of macrophages, enhanced release of oxygen radicals, microbial killing, enhanced expression of MHC Class II molecules, anti-viral effects, induction of the inducible nitric oxide synthase gene and release of NO, chemotactic factors to recruit and activate immune effector cells, down regulation of transferrin receptors limiting microbial access to iron necessary for survival of intracellular pathogens, etc. Genetically engineered mice that lack interferon-γ or its receptor are extremely susceptible to mycobacterial infection.
Recombinant INF-γ was administered to normal volunteers and cancer patients in the 1980s through intramuscular and subcutaneous routes. There was evidence of monocyte activation, e.g. release of oxidants. Jaffe et al. reported rINFγ administration to 20 normal volunteers. (See, Jaffe et al., J Clin Invest. 88, 297-302 (1991)) First, they gave rINF-γ 250 μg subcutaneously noting peak serum levels at 4 hours and a trough at 24 hours.
Several clinical trials were sponsored to evaluate INF-γ for infectious diseases. The MDR-TB clinical trial, entitled “A Phase II/III Study of the Safety and Efficacy of Inhaled Aerosolized Recombinant Interferon-γ 1 b in Patients with Pulmonary Multiple Drug Resistant Tuberculosis (MDR-TB) Who have Failed an Appropriate Three Month Treatment,” enrolled 80 MDR-TB patients at several sites (Cape Town, Port Elizabeth, Durban, Mexico) and randomized them to receive aerosol rINF-γ (500 μg MWF) or placebo for at least 6 months in addition to second line therapy. This clinical trial was stopped prematurely due to lack of efficacy on sputum smears, M tb culture, or chest radiograph changes.
Ziesche et al. gave rINF-γ subcutaneously at a dose of 200 mg three times a week in addition to oral prednisone to 9/18 patients with idiopathic pulmonary fibrosis (IPF). See, Ziesche et al., (1999) N. Eng. J. Med., 341, 1264-1269). The results of a subsequent phase 3 clinical trial of interferon γ-1b therapy for IPF were recently published. Although this was the first clinical trial of IPF that had an adequate sample size and was a randomized, prospective, double-blind, placebo-controlled study, no significant effect on markers of physiologic function, such as forced vital capacity, was observed. However, more deaths occurred in the placebo group, and survival was significantly better for a subset of patients who received interferon γ-1b therapy and had a forced vital capacity of 55% or greater and diffuse lung capacity for carbon monoxide of 35% or greater of the normal predicted values. The discordance between disease progression and survival in that study remains to be explained. One possibility is that interferon γ-1b therapy improves host defense against infection and diminishes the severity of lower respiratory tract infection when it complicates the clinical course of patients with IPF. This possibility is supported by the observation by Strieter et al. that the interferon-inducible CXC chemokine, I-TAC/CXCL11, which has antimicrobial properties, was significantly up-regulated in plasma and bronchoalveolar lavage (BAL) fluid in individuals who received interferon γ-1b compared to those who received placebo, whereas profibrogenic cytokines were generally not significantly altered by interferon γ-1b therapy over a 6-month treatment period. (See, Strieter et al., Am J Respir Crit Care Med. (2004). One possibility to explain the lackluster results is inadequate levels of drug delivered to the lung interstitium with current dosing strategies.